It is well known to convert alkylene oxide into a cyclic alkylene carbonate in the presence of a suitable catalyst. Such processes have been described for example in U.S. Pat. No. 4,508,927 and U.S. Pat. No. 5,508,442. These patents describe processes in which an alkylene oxide is reacted with carbon dioxide in the presence of a catalyst to form the cyclic alkylene carbonate. The catalyst can be an organic phosphonium halide as described in U.S. Pat. No. 4,508,927, a metal halide as described in U.S. Pat. No. 5,508,442, or an organic trisubstituted phosphine as described in Japanese patent application No. 73022702.
A process for hydrolyzing cyclic alkylene carbonates to produce a diol and carbon dioxide, more specifically to produce 1,2-propanediol, has been disclosed in WO-A 2004/056793. This reference describes a process for the preparation of 1,2-propanediol from propylene oxide, which process comprises: (a) contacting propylene oxide with carbon dioxide in the presence of a homogeneous phosphorus comprising catalyst to obtain propylene carbonate, (b) optionally removing at least part of the carbon dioxide, (c) adding water to the reaction product comprising propylene carbonate and phosphorus comprising catalyst and contacting the mixture with a heterogeneous catalyst to obtain 1,2-propanediol in combination with dialkyl carbonate and/or carbon dioxide, and (d) separating 1,2-propanediol from the reaction product obtained.
This process requires a considerable amount of energy. It would therefore be an advancement in the art to obtain an improvement of the method of the above process, to more efficiently control the energy balance of the process.